Conventionally, in a variety of fields, aspiration apparatuses are used for aspirating and measuring a specific volume of an object such as liquid. In particular, an aspiration apparatus is frequently used with an aspiration tip connected to a leading end thereof in, for example, biochemical experiments (Japanese Unexamined Patent Publication No. 2002-98706). The aspiration tip is used as a jig and including a main body portion which is substantially in the form of a cylinder having a tubular passage defining an aspiration path for aspirating an object, one end of the tubular passage being formed with an aspiration opening for aspirating liquid or the like. Another opening is formed in the other end of the aspiration tip to which a nozzle section of the aspiration apparatus for generating an aspiration force is attached.
Examples of the object include not only liquids, but also powder, particles, or biological cells included in a liquid. In the case that the object is a cell, it is possible, by selecting cells based on their shapes by operating the aspiration apparatus to which the aspiration tip is connected, to reduce the deviation of experimental conditions in a variety of experiments that are to be performed using the selected cells. The selected cells can be used for high-throughput screening (HTS), for example.
By the way, the conventional aspiration tip generates a discharging force in the tubular passage of the aspiration tip before the aspiration to preliminarily discharge part of air and, thereafter, a pump mechanism is driven to generate an aspiration force in the tubular passage to aspirate the object, with the aspiration opening being in proximity to or in contact with the object. At the time of discharge, a discharging force is generated in the tubular passage again to discharge the object with air. Thus, the conventional aspiration tip aspirates and discharges the object due to pressure fluctuations inevitable to movements of air in the tubular passage.
In recent years, a technique for accurately aspirating and discharging a very small amount of an object has been required. However, in the case of using the conventional aspiration tip, there is a problem that it is difficult to aspirate and discharge a very small amount of an object efficiently and accurately because volume fluctuations occur owing to contraction and expansion of air or the like in the tubular passage at the time of the aspiration and the discharge. Specifically, for example, in the case that a liquid having a high viscosity is aspirated or discharged, the air in the tubular passage expands or contracts, so that the aspiration speed or the discharge speed (i.e. response to the operation for aspiration or discharge) is liable to decrease, which results in a low working efficiency. Further, in the case that a liquid having a high viscosity, a cell culture solution including impurities or the like is discharged, a portion of the liquid is liable to adhere to and remain on the inner wall surface. In this case, the object is not completely discharged, so that it cannot be measured accurately. Further, in the case that the aspiration tip is used repeatedly with a part of the object remaining in the tubular passage, sample contamination is liable to occur between the samples that have been successively taken. In addition, when the object is observed with an observation device such as a microscope while the object is held in the aspiration tip, for example, the air in the tubular passage may reduce the observation accuracy.